The present invention relates to an ultrasonic motor having a force applying means for applying a force to a vibrating member and moving member, and more particularly to an ultrasonic motor having a force applying means for applying a force to be adjusted before or after assembling the vibrating member, moving member and so on, and to an electronic apparatus with such a ultrasonic motor.
In the field of micro-motors, attention has recently been drawn to ultrasonic motors that utilize a piezoelectric effect provided by a piezoelectric element.
There is known, as one example of such an ultrasonic motor, a type that is provided with a support plate, a center shaft fixed to the support plate, a vibrating member fixed on the center shaft, a piezoelectric element joined to an underside of the vibrating member, a moving member placed in abutment against a projection provided on the vibrating member, and a force applying means placed in pressure contact with the moving member.
According to this art, the piezoelectric element is vibrated so that the vibration of the piezoelectric element causes the vibrating member to elastically vibrate. Through this elastic vibration, the projection of the vibrating member is brought into contact with the moving member, with a certain periodicity. Meanwhile, the force applying means applies a force to the moving member and the projection on the vibrating member to generate a frictional force between the moving member and the vibrating member, thus driving the moving member through the frictional force.
Here, it is known that the force applying means includes, in kind, a leaf spring 101 as shown in FIG. 11A or a dish-shaped spring 102 as shown in FIG. 11B, and one formed by a spacer for adjusting the force of the dish-shaped spring (see Japanese Patent Laying-open No H2-287281 and Japanese Patent Laying-open No S63-305770).
In the case of the leaf spring 101, however, there is encountered a variation in force due to a shape of the leaf spring, variation in thickness thereof, variation in thickness of parts such as the vibrating member and the moving member, and variation caused by assembling these parts. Such variation in force in turn causes change in the frictional force between the vibrating member and the moving member and also the drive force to the moving member, thus posing a problem of causing variation in individual characteristics of the ultrasonic motor.
On the other hand, where using the dish-shaped spring 102 and the spacer, the force can be adjusted by adjusting the variation in such parts as the dish-shaped spring, vibrating member and moving member, through controlling a spacer thickness. Nevertheless, the force adjustment still requires troublesome operations, such as combining parts due to thickness selection before assembling and disassembling for motor characteristic inspection after assembling, e.g., changing the number of spacers. Furthermore, the adjustment with spacers, even if there is slight difference in thickness, induces greater variation in force applied. Due to this, it is impossible to accurately adjust the force, resulting in such problems as increase in size and decrease in efficiency of the apparatus.